Recently, with the advent of a smartphone and a smart TV, the use of video data through a wired/wireless communication network tends to grow explosively. Since video data has an excellent information delivery ability but a very large capacity, compared to general text data, the video data has difficulties in being transmitted or replayed and stored on a network channel having a limited bandwidth. In addition, since vast video information is appropriately processed according to requirement of an application, a system for processing a video also requires a high specification.
The video encoding includes lossy coding and lossless coding. H.264/AVC supports the lossless coding in addition to the lossy coding. In particular, for the lossless encoding, a more efficient lossless coding technique has been adopted in H.264/AVC Fidelity Range Extension (FRExt) standardization. The lossless encoding technique that has been adopted in FRExt does not just perform transformation and quantization in order to prevent loss of data. That is, lossless compression may be performed by performing entropy coding directly on residual signals found through intra-prediction and inter-prediction, without transformation and quantization.
In addition, standardization for high efficient video coding (HEVC) has recently been completed as next-generation video compression standard technology that is known to have compression efficiency approximately twice as great as conventional H.264/AVC.
HEVC defines a coding unit (CU), a prediction unit (PU), and a transform unit (TU), which form a quadtree structure, and applies an additional in-loop filter such as a sample adaptive offset (SAO) and a deblocking filter. In addition, HEVC enhances a compression encoding efficiency by improving the existing intra-prediction and inter-prediction.
In the intra-prediction, encoding is performed using, as a prediction value for a pixel currently intended to be encoded, a value of a pixel around the current pixel directly or a value generated by performing processes such as a filtering on several pixels around the current pixel. In addition, a difference between a value generated through the prediction and a value of the current pixel is transmitted and encoded along with other additional information (information regarding an intra-prediction mode, for example, a DC mode, a horizontal direction mode, or a vertical direction mode).
Here, in order to determine a prediction value of a current block, the intra-prediction uses a boundary pixel of a neighbor block that has ever been encoded and then reconstructed. However, the intra-prediction method has a limitation in that a prediction error increases as a distance between a reference pixel and a current pixel increases.
Furthermore, when the intra-prediction is not performed well despite any intra-prediction mode depending on characteristics of a video, a difference that should be transmitted to a decoding apparatus is increased, thus resulting in reduction of an encoding efficiency. In particular, for a complicated region in which a DC mode is applied, since the intra-prediction is performed using an average value of pixels around the current pixel, it is difficult to accurately predict the current pixel. That is, since a difference between a value of the current pixel and its prediction value increases, the encoding efficiency may be lowered.
Furthermore, for a planar mode according to the HEVC, when the current pixel is positioned further inward, a distance between the current pixel and the reference pixel increases and accuracy of the prediction is reduced.